Moisture detection is important in a number of different situations. Moisture is undesirable whether it appears in houses, textiles, packaging materials, electronic appliances, chemicals, dry foodstuffs, etc. Our industrialized society produces increasingly refined products, many of which are highly sensitive to moisture.
A plurality of prior art devices for detecting moisture are available on the market. WO0016081 discloses an electronic sensor comprising a resonant circuit. The resonant circuit comprises, inter alia, electrically conductive particles and a material that is capable of swelling in the presence of moisture. When the material swells the conductive particles are drawn apart and the conductivity of the moisture sensitive material decreases and the electrical resistance of the material increases. The electronic sensor is read by means of a detector, which generates an electromagnetic field.
U.S. Pat. No. 5,463,377 discloses a sensor comprising a circuit with two electrodes connected to a switch. The switch closes in the presence of an electrically conductive liquid between the electrodes. The switch may also close by a change in conductivity of a material between the electrodes or by expansion of a liquid absorber that pushes the electrodes together.
U.S. Pat. No. 6,097,297 discloses a sensor that is in permanent contact with the detector. The sensor comprises two conductive electrode strips which have an absorbing material located between them. When a liquid, preferably urine, is absorbed, the resistance between the electrodes changes, which sends a signal to the detector.
GB 2,183,344 discloses, inter alia, a sensor for detecting moisture. The sensor comprises a ceramic substrate with a tin oxide film, the substrate being connected on both sides to platinum electrodes. In the presence of moisture, the electrical conductivity across the substrate changes, which is detected by means of the electrodes.
U.S. Pat. No. 4,327,731 discloses a system for indicating moisture in a diaper comprising an enzyme and a substrate as well as a chromogen. In the presence of moisture, the substrate is dissolved, which catalyses reactions with the enzyme and the chromogen resulting in a coloured pigment being produced.
WO 9956690 concerns an incontinence pad based on the above-mentioned technique disclosed in U.S. Pat. No. 4,327,731. The pad is divided into zones which have varying urine absorption capacity and which undergo colour changes when exposed to moisture, thereby permitting a quantitative estimate of urine incontinence to be indicated.
In addition, there are sensors comprising an enzyme and a substrate that are adapted for other fields of use, such as the sensor disclosed in WO 0125472, which is an activable time-temperature indicator for determining and/or controlling the durability status of a product. The enzyme in this sensor is activated at a time 0 by being brought into contact with the substrate, for example in connection with the packaging of the finished product.